Single-mirror two-axis displacement measurement method and device applied to scanning interference field

Abstract

The application provides a single-mirror two-axis displacement measurement method and device applied to a scanning interference field, comprising: outputting difference frequency laser with vertical orthogonal polarization, the difference frequency laser comprising first polarization laser with a first frequency and second polarization laser with a second frequency, the first polarization laser being horizontally polarized and the second polarization laser being vertically polarized; the first polarization laser is reflected by a first plane mirror and enters a first photoelectric detector as reference light; the second polarization laser is reflected by a second plane mirror and a third plane mirror and enters a second photoelectric detector as measurement light; wherein the bias angle of the first plane mirror is zero, the bias angle of the second plane mirror is not zero, and the bias angle of the third plane mirror is 2; based on the interference between the measurement light and the reference light, the displacement of the measured object in a two-dimensional plane is calculated. The application cooperates with a single-axis laser interferometer to realize the displacement measurement of two degrees of freedom in a plane by using only a single measurement mirror.

Description

Technical Field

[0001] This application relates to the field of optical interferometry technology, and more specifically, to a single-mirror biaxial displacement measurement method and apparatus for scanning interferometric fields. Background Technology

[0002] In the field of precision measurement, laser interferometric displacement measurement technology is widely used to detect two-degree-of-freedom displacements within an object's surface at the nanometer level or even higher precision due to its extremely high accuracy and resolution.

[0003] like Figure 1 The diagram shows the principle of a dual-mirror dual-axis displacement measuring device in traditional technology, which consists of an X-direction laser interferometer 01, an X-direction measuring mirror 03, a Y-direction laser interferometer 02, a Y-direction measuring mirror 04, and a worktable 05.

[0004] Scanning interference field exposure is a key technology for manufacturing large-size gratings. During the manufacturing process of large-size gratings, the X-axis displacement reaches 650 mm, and the Y-axis displacement reaches 1700 mm. Using methods such as... Figure 1 The XY dual-mirror dual-axis displacement measuring device shown requires a Y-axis measuring mirror (weighing approximately 200kg) with a length of 1700mm to be installed along the X-axis at the edge of the upper stage. This measurement method has the following technical drawbacks: ① Additional burden of off-center loading: The installation of the Y-axis measuring mirror introduces an asymmetrical load to the workpiece stage, reducing its dynamic stability and affecting the uniformity of its running speed. ② Space occupation and operational obstacles: Due to the large size of the Y-axis measuring mirror, a wider upper stage and a longer guide rail are required, which also seriously hinders the loading, installation, and unloading of the grating substrate. ③ System complexity and error accumulation: The optical and mechanical structure of the equipment is significantly increased, and two sets of laser interferometers along the X and Y axes need to be deployed. The negative impact of their zero-point error and integral accumulation error on the displacement measurement accuracy cannot be ignored. ④ Edge data loss: At the overlapping position of the X-axis measuring mirror 03 and the Y-axis measuring mirror 04, the Y-axis laser interferometer 02 cannot acquire data, resulting in the loss of measurement data. Due to the above drawbacks, a large number of surface shape errors are introduced during the manufacturing process of gratings, which directly leads to a sharp drop in the quality of the grating diffraction wavefront, making it unable to meet the requirements for use. Summary of the Invention

[0005] The purpose of this application is to provide a single-mirror biaxial displacement measurement method and apparatus for scanning interferometric fields, which can solve at least one of the aforementioned technical problems. The specific solution is as follows:

[0006] This application provides a single-mirror biaxial displacement measurement method applied to scanning interferometric fields, including:

[0007] The output is a difference-frequency laser with vertical orthogonal polarization, the difference-frequency laser including a first polarized laser with a first frequency and a second polarized laser with a second frequency, the first polarized laser being horizontally polarized and the second polarized laser being vertically polarized;

[0008] The first polarized laser beam, after being reflected by the first plane mirror, is used as reference light and enters the first photodetector; the second polarized laser beam, after being reflected by the second and third plane mirrors, is used as measurement light and enters the second photodetector; wherein, the bias angle of the first plane mirror is zero, and the bias angle of the second plane mirror is... The offset angle of the third plane mirror is not zero, and the offset angle is 2. ;

[0009] Based on the interference between the measuring light and the reference light, the displacement of the object under test along the X direction in the two-dimensional plane is calculated. and displacement along the Y direction ,in,

[0010]

[0011] λ R The center wavelength of the difference frequency laser. This causes a phase change when moving in the X direction. The phase change is generated by the movement in the Y direction. The offset angle of the second plane mirror.

[0012] In some embodiments, the offset angle of the second planar reflector It ranges from 0.05° to 1°.

[0013] In some embodiments, the first polarized laser, after being reflected by the first planar mirror, is used as reference light and incident on the first photodetector, including:

[0014] The first polarized laser is reflected sequentially by the first beam splitter, the polarization beam splitter, and the first plane mirror, and then passes through the polarization beam splitter and the first beam splitter again before entering the first photodetector.

[0015] In some embodiments, the second polarized laser, after being reflected by the second and third plane mirrors, is used as measurement light and incident on the second photodetector, including:

[0016] The second polarized laser sequentially passes through the first beam splitter, the polarization beam splitter, the quarter-wave plate, and the second plane mirror. After being reflected by the quarter-wave plate again, its polarization state becomes horizontal. It then passes through the polarization beam splitter again, is reflected by the third plane mirror, and returns along the same path. Finally, it passes through the first beam splitter and enters the second photodetector.

[0017] In some embodiments, the distance between the second plane mirror and the polarizing beam splitter is greater than the distance between the first plane mirror and the third plane mirror and the polarizing beam splitter.

[0018] In some embodiments, it also includes:

[0019] The second planar reflector is rigidly connected to the two-dimensional plane of the object under test, so that the displacement of the object under test in the two-dimensional plane in the X and Y directions is measured by measuring the displacement of the second planar reflector in the two-dimensional plane.

[0020] In some embodiments, it also includes:

[0021] The first polarized laser and the second polarized laser enter the first photodetector through the first beam splitter to form a reference interference signal.

[0022] In some embodiments, the output vertically orthogonally polarized difference-frequency laser is a dual-frequency laser or two independent single-frequency lasers.

[0023] In some embodiments, when the output difference-frequency laser with perpendicular orthogonal polarization is two independent single-frequency lasers, a second beam combiner prism is further included, through which the reference light and the measurement light are incident on the second photodetector.

[0024] This application also provides a single-mirror biaxial displacement measurement device for scanning interferometric fields, comprising:

[0025] A laser that outputs a difference-frequency laser with perpendicular orthogonal polarization, the difference-frequency laser comprising a first polarized laser with a first frequency and a second polarized laser with a second frequency, the first polarized laser being horizontally polarized and the second polarized laser being vertically polarized;

[0026] A first photodetector is used to receive the reference interference signal formed by the difference frequency laser.

[0027] The second photodetector is used to receive the reference light and the measurement light to form a measurement interference signal;

[0028] The reference optical path includes a first beam splitter, a polarizing beam splitter, and a first plane mirror; the first polarized laser is reflected sequentially by the first beam splitter, the polarizing beam splitter, and the first plane mirror, and then passes through the polarizing beam splitter and the first beam splitter again as reference light before entering the first photodetector.

[0029] The measurement optical path includes a first beam splitter, a polarizing beam splitter, a quarter-wave plate, a second plane mirror, and a third plane mirror. The second polarized laser sequentially passes through the first beam splitter, the polarizing beam splitter, the quarter-wave plate, and the second plane mirror for reflection, then passes through the quarter-wave plate again, where its polarization state becomes horizontal. After passing through the polarizing beam splitter again, it is reflected back through the third plane mirror and returns along the original path, serving as the measurement light. It then passes through the first beam splitter and is coaxially incident on the second photodetector with the reference light.

[0030] Wherein, the offset angle of the first plane mirror is zero, and the offset angle of the second plane mirror is... The offset angle of the third plane mirror is not zero, and the offset angle is 2. ;

[0031] Based on the interference between the measuring light and the reference light, the displacement of the object under test along the X direction in the two-dimensional plane is calculated. and displacement along the Y direction ,in,

[0032]

[0033] λ R The center wavelength of the difference frequency laser. This causes a phase change when moving in the X direction. The phase change is generated by the movement in the Y direction. The offset angle of the second plane mirror.

[0034] Compared with the prior art, the above-described solutions of this application have at least the following beneficial effects:

[0035] This application proposes a single-mirror dual-axis displacement measurement method and apparatus for scanning interferometric fields. This method, in conjunction with a single-axis laser interferometer, can achieve in-plane two-degree-of-freedom displacement measurement using only a single measuring mirror, simultaneously calculating displacement information in both the horizontal and vertical directions. This significantly reduces the number and size of interferometric mirrors required in large displacement measurement systems, thereby effectively reducing the overall system size and structural complexity. This application is applicable to high-end equipment such as scanning exposure fields and lithography machines that require large-stroke movements in a two-dimensional plane. Compared to traditional dual-mirror dual-axis systems, this application can improve system integration and measurement accuracy while reducing the number of measuring mirrors, possessing significant engineering application value. Attached Figure Description

[0036] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0037] Figure 1 This is a schematic diagram of the principle of a traditional dual-mirror dual-axis displacement measuring device.

[0038] Figure 2 These are schematic diagrams illustrating the principle of a single-mirror biaxial displacement measurement device based on scanning exposure technology, as shown in some embodiments.

[0039] Figure 3 These are schematic diagrams of scanning interference field exposures shown in some embodiments.

[0040] Figure 4 These are schematic diagrams of the structure of a single-mirror biaxial displacement measuring device as shown in some embodiments.

[0041] Figure 5 These are schematic diagrams illustrating the single-mirror biaxial displacement measurement method in some embodiments.

[0042] Figure 6 This is a schematic diagram of the structure of a single-mirror biaxial displacement measuring device shown in some other embodiments.

[0043] Figure 7 This is a schematic diagram of the principle of a single-mirror dual-axis displacement measuring device.

[0044] Figure 8 This is a simulation diagram of the second plane mirror without tilt angle.

[0045] Figure 9 This is a simulation diagram when the second plane mirror has a tilt angle.

[0046] Explanation of reference numerals in the attached figures:

[0047] X-direction laser interferometer 01, X-direction measuring mirror 03, Y-direction laser interferometer 02, Y-direction measuring mirror 04, worktable 05;

[0048] Light source 31, beam splitter 32, first reflector 33, third reflector 34, second reflector 35, fourth reflector 36, dual-frequency laser interferometer 37, second plane reflector 38, grating substrate 39;

[0049] Laser 71, first polarizing laser 711, second polarizing laser 712, first beam splitter 72, first beam combiner 721, second beam combiner 722, first photodetector 73, polarizing beam splitter 74, first plane mirror 75, quarter-wave plate 76, third plane mirror 77, second photodetector 78. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0051] Traditional in-plane two-degree-of-freedom laser interferometry schemes generally employ an interferometric system structure based on dual measurement axes, using two independent interferometer optical paths to measure displacements in mutually orthogonal directions. While traditional laser interferometric two-dimensional displacement measurement schemes based on dual mirrors can achieve nanometer-level high-precision measurements, their core technical problem lies in the inherent complexity of their system architecture. Because the two mirrors are necessarily physically separated, the measurement reference they form is not the same ideal point. When the measured object exhibits unavoidable minute angular pendulum motion, it directly leads to severe Abbe errors, which are coupled with the displacement signal and are difficult to completely eliminate through subsequent algorithms.

[0052] Based on this, this application proposes a single-mirror dual-axis displacement measurement method and device based on scanning exposure technology. It establishes a single-mirror dual-axis displacement measurement principle for a two-dimensional workpiece stage, setting a specific angle between the X-axis single-axis measuring mirror and the Y-axis. X and Y coordinate values ​​at arbitrary positions are acquired through step scanning, achieving XY orthogonal dual-axis measurement and avoiding zero-point error and integral accumulation error in dual-mirror systems. Only a 650mm X-axis single-axis measuring mirror is needed to acquire dual-axis displacement data, reducing the interference of the Y-axis measuring mirror load on the workpiece stage performance. Furthermore, online calculation technology is employed to simultaneously acquire XY dual-axis displacement data, improving measurement efficiency and reliability. This significantly reduces the number and size of interference mirrors required in large displacement measurement systems, thereby effectively reducing the overall system size and structural complexity.

[0053] The optional embodiments of this application are described in detail below with reference to the accompanying drawings.

[0054] like Figure 2 , Figure 3As shown in the schematic diagram, the single-mirror dual-axis displacement measurement system based on the scanning exposure process proposed in this application generates two beams after the light source 31 passes through the beam splitter 32. These beams propagate through the first reflecting mirror 33, the second reflecting mirror 35, the third reflecting mirror 34, and the fourth reflecting mirror 36, respectively, and then form interference field fringes on the surface of the grating substrate 39. The stage 05 carries the grating substrate 39 and performs scanning in the Y direction and stepping motion in the X direction. The dual-frequency laser interferometer 37 and the second plane reflecting mirror 38 form an interferometric measurement module, responsible for providing two degrees of freedom displacement in the X and Y directions.

[0055] The scanning beam interference lithography system is based on the principle of forming interference fringes by the interference of two small-diameter Gaussian beams. The specific process is as follows: First, the two-dimensional precision stage 05 moves along the Y-direction, i.e., scanning along the direction parallel to the interference fringes. During this process, the stage 05 displacement measurement system measures the X and Y-direction displacements of the two-dimensional precision stage driving the grating substrate 39 to move on the horizontal plane. The phase measurement system measures the phase distribution of the interference fringes of the exposure beam. The phase-locking system modulates the phase distribution of the interference fringes to compensate for changes in the phase distribution caused by air disturbances, optical platform vibrations, etc., completing the tracking of the interference fringes and the grating substrate during the scanning exposure process. After completing this scan, the two-dimensional precision stage moves along the X-direction, i.e., stepping perpendicular to the interference fringes. During this process, the phase-locking system modulates the phase distribution of the interference fringes to achieve phase alignment and stitching of the interference fringes perpendicular to the fringe direction. Then, the two-dimensional precision stage continues to scan and expose along the Y-direction. This process is repeated to complete the entire grating exposure.

[0056] In some embodiments, such as Figure 4 As shown, this application provides a single-mirror biaxial displacement measurement device for scanning interferometric fields, comprising:

[0057] Laser 71 outputs a difference-frequency laser with perpendicular orthogonal polarization. The difference-frequency laser includes a first polarized laser with a first frequency and a second polarized laser with a second frequency. The first polarized laser is horizontally polarized, and the second polarized laser is vertically polarized.

[0058] The first photodetector 73 is used to receive the reference interference signal formed by the difference frequency laser.

[0059] The second photodetector 78 is used to receive the reference light and the measurement light to form a measurement interference signal;

[0060] The reference optical path includes a first beam splitter 72, a polarizing beam splitter 74, and a first plane mirror 75. The first polarized laser is reflected sequentially by the first beam splitter 72, the polarizing beam splitter 74, and the first plane mirror 75, and then passes through the polarizing beam splitter 74 and the first beam splitter 72 again as reference light before entering the first photodetector 73.

[0061] The measurement optical path includes a first beam splitter 72, a polarizing beam splitter 74, a quarter-wave plate 76, a second plane mirror 38, and a third plane mirror 77. The second polarized laser sequentially passes through the first beam splitter 72, the polarizing beam splitter 74, the quarter-wave plate 76, and the second plane mirror 38 for reflection, and then passes through the quarter-wave plate 76 again, where its polarization state becomes horizontally polarized. It then passes through the polarizing beam splitter 74 again, and is reflected back through the third plane mirror 77, returning along the original path. As the measurement light, it passes through the first beam splitter 72 and is coaxially incident on the second photodetector 78 with the reference light.

[0062] Wherein, the offset angle of the first plane mirror 75 is zero, and the offset angle of the second plane mirror 38 is zero. The offset angle of the third plane mirror 77 is not zero, and the offset angle is 2. ;

[0063] Based on the interference between the measuring light and the reference light, the displacement of the object under test along the X direction in the two-dimensional plane is calculated. and displacement along the Y direction ,in,

[0064]

[0065] λ R The center wavelength of the difference frequency laser. This causes a phase change when moving in the X direction. The phase change is generated by the movement in the Y direction. The offset angle of the second plane mirror.

[0066] This application, in conjunction with a single-axis laser interferometer, enables in-plane two-degree-of-freedom displacement measurement using only a single measuring mirror (the second plane mirror), allowing simultaneous calculation of displacement information in the X and Y vertical directions within the horizontal plane. This significantly reduces the number and size of interferometric mirrors required in large displacement measurement systems, thereby effectively reducing the overall system size and structural complexity.

[0067] like Figure 5 As shown, this application provides a single-mirror biaxial displacement measurement method applied to scanning interferometric fields, including the following method steps:

[0068] Step S102: Output a difference-frequency laser with vertical orthogonal polarization, wherein the difference-frequency laser includes a first polarized laser with a first frequency and a second polarized laser with a second frequency, the first polarized laser being horizontally polarized and the second polarized laser being vertically polarized;

[0069] Step S104: The first polarized laser, after being reflected by the first plane mirror, is used as reference light and enters the first photodetector; the second polarized laser, after being reflected by the second and third plane mirrors, is used as measurement light and enters the second photodetector; wherein, the bias angle of the first plane mirror is zero, and the bias angle of the second plane mirror is... The offset angle of the third plane mirror is not zero, and the offset angle is 2. ;

[0070] Step S106: Based on the interference between the measurement light and the reference light, calculate the displacement of the object under test along the X direction in the two-dimensional plane. and displacement along the Y direction ,in,

[0071]

[0072] λ R The center wavelength of the difference frequency laser. This causes a phase change when moving in the X direction. The phase change is generated by the movement in the Y direction. The offset angle of the second plane mirror.

[0073] This application proposes a single-mirror, dual-axis displacement measurement method for scanning interferometric fields. This method, in conjunction with a single-mirror laser interferometer, can achieve in-plane two-degree-of-freedom displacement measurement using only a single measuring mirror (the second plane mirror), simultaneously calculating displacement information in the X and Y directions within the horizontal plane. This significantly reduces the number and size of interferometric mirrors required in large displacement measurement systems, thereby effectively reducing the overall system size and structural complexity.

[0074] This application is applicable to high-end equipment such as scanning exposure fields and lithography machines that require large-stroke movements within a two-dimensional plane. Compared to traditional dual-mirror, dual-axis systems, this application can improve system integration and measurement accuracy while reducing the number of measuring mirrors, thus possessing significant engineering application value. In some embodiments, such as Figure 4 As shown, the offset angle of the second plane mirror 38 It ranges from 0.05° to 1°. The offset angle is... This is the angle between the second plane mirror 38 and the X-direction, that is, the angle between the second polarized laser and the normal direction of the second plane mirror 38. The second polarized laser is not incident perfectly perpendicularly on the second plane mirror 38. (Angle) If the angle is too large, the reflected light will not be able to return along the original optical path and interfere with the reference light, so the angle should not be too large.

[0075] In some embodiments, laser 71 is a dual-frequency laser that outputs a difference-frequency laser with vertical orthogonal polarization. The difference-frequency laser includes a first polarized laser with a first frequency and a second polarized laser with a second frequency. The first polarized laser is horizontally polarized, and the second polarized laser is vertically polarized.

[0076] The laser beam emitted from laser 71, after passing through the first beam-splitting prism 72, is reflected and enters the first photodetector 73 to form a reference interference signal, which is used to adjust the laser signal output by laser 71. The laser beam from laser 71, after passing through the first beam-splitting prism 72, enters the polarizing beam-splitting prism 74. The parallel polarized light is transmitted and then perpendicularly incident on the first plane mirror 75 (i.e., the reference mirror). It then returns along the same path, passing through the polarizing beam-splitting prism 74 for transmission and the first beam-splitting prism 72 for reflection, before entering the second photodetector 78 as reference light. After passing through the first beam-splitting prism 72, it enters the polarizing beam-splitting prism 74. The perpendicularly polarized light is reflected by the polarizing beam-splitting prism 74, passes through a quarter-wave plate 76, and then enters the second plane mirror 38 (i.e., the bias mirror). The reflected light passes through the quarter-wave plate 76 again. Since the polarization state changes to parallel polarization after passing through the quarter-wave plate 76 twice, it is transmitted through the polarizing beam-splitting prism 74 and then enters the third plane mirror 77 (i.e., the bias reference mirror). The bias angle of the third plane mirror 77 is twice that of the second plane mirror 38, so the beam is incident perpendicularly onto the third plane mirror 77 and then returns along the same path. During this process, it passes sequentially through the polarizing beam splitter 74, the quarter-wave plate 76, the second plane mirror 38, and the quarter-wave plate 76 again. It also passes through the quarter-wave plate 76 twice during this process, thus changing its polarization state to perpendicular polarization. Then, it is reflected by the polarizing beam splitter 74, and subsequently reflected by the first beam splitter 72 into the second photodetector 78, where it coincides with the reference beam to form a measurement interference signal.

[0077] In some embodiments, the distance between the second plane mirror 38 and the polarizing beam splitter 74 is greater than the distance between the first plane mirror 75 and the polarizing beam splitter 74, and also greater than the distance between the third plane mirror 77 and the polarizing beam splitter 74. Since the second plane mirror 38 is rigidly connected to the surface of the object under test, and the pose of the object under test is reflected by the pose of the second plane mirror 38, the object under test is often far from the polarizing beam splitter 74. The first plane mirror 75 is used to provide a reference optical path, and the third plane mirror 77 is used to provide a reflected signal. Keeping the distances between the first plane mirror 75, the third plane mirror 77, and the polarizing beam splitter 77 small can reduce the size of the measuring device.

[0078] In some embodiments, the single-mirror biaxial displacement measurement method further includes: rigidly connecting the second plane mirror 38 to the two-dimensional plane of the object under test, such that the displacement of the object under test in the two-dimensional plane in the X and Y directions is measured by measuring the displacement of the second plane mirror 38 in the two-dimensional plane in the X and Y directions.

[0079] In some embodiments, such as Figure 6 As shown, the single-mirror biaxial displacement measurement device applied to scanning interferometric fields in this application includes:

[0080] The first polarizing laser 711 and the second polarizing laser 712 respectively output difference-frequency lasers with perpendicular orthogonal polarization. The difference-frequency lasers include a first polarizing laser with a first frequency and a second polarizing laser with a second frequency. The first polarizing laser is horizontally polarized and the second polarizing laser is vertically polarized.

[0081] The first beam combiner prism 721 and the first photodetector 73 are used to receive the difference frequency laser forming reference interference signal;

[0082] The second beam combiner prism 722 and the second photodetector 78 are used to receive the reference light and the measurement light to form a measurement interference signal;

[0083] The reference optical path includes a first beam splitter 72, a polarizing beam splitter 74, and a first plane mirror 75. The first polarized laser is reflected sequentially by the first beam splitter 72, the polarizing beam splitter 74, and the first plane mirror 75, and then passes through the polarizing beam splitter 74 and the first beam splitter 72 again as reference light before entering the first photodetector 73 through the second beam combiner 722.

[0084] The measurement optical path includes a first beam splitter 72, a polarizing beam splitter 74, a quarter-wave plate 76, a second plane mirror 38, and a third plane mirror 77. The second polarized laser sequentially passes through the first beam splitter 72, the polarizing beam splitter 74, the quarter-wave plate 76, and the second plane mirror 38 for reflection, and then passes through the quarter-wave plate 76 again, where its polarization state becomes horizontally polarized. It then passes through the polarizing beam splitter 74 again, and is reflected back through the third plane mirror 77, returning along the original path. As the measurement light, it passes through the first beam splitter 72 and the second beam combiner 722, and coaxially enters the second photodetector 78 with the reference light.

[0085] Wherein, the offset angle of the first plane mirror 75 is zero, and the offset angle of the second plane mirror 38 is zero. The offset angle of the third plane mirror 77 is not zero, and the offset angle is 2. ;

[0086] Based on the interference between the measuring light and the reference light, the displacement of the object under test along the X direction in the two-dimensional plane is calculated. and displacement along the Y direction ,in,

[0087]

[0088] λ R The center wavelength of the difference frequency laser. This causes a phase change when moving in the X direction. The phase change is generated by the movement in the Y direction. The offset angle of the second plane mirror.

[0089] The optical propagation process is as follows: the first polarization laser 711 emits vertically polarized light with a frequency of f1, which, after passing through the first beam splitter 72, is reflected and then enters the first photodetector 73 after passing through the first beam combiner 721; the second polarization laser 712 emits horizontally polarized light with a frequency of f2, which, after passing through the first beam splitter 72, is reflected and then enters the first photodetector 73 after passing through the first beam combiner 721. The two beams of light are combined in the first photodetector 73 to form a reference interference signal.

[0090] The first polarizing laser 711 emits vertically polarized light with a frequency of f1. After passing through the first beam splitter 72, the transmitted light passes through the polarizing beam splitter 74 and is reflected into the quarter-wave plate 76, then enters the second plane mirror 38. The reflected light passes through the quarter-wave plate 76 again. Since the polarization state changes to parallel polarization after passing through the waveplate twice, it is transmitted through the polarizing beam splitter 74 and then enters the third plane mirror 77. The bias angle of the third plane mirror 77 is twice that of the second plane mirror 38, so the beam enters the third plane mirror 77 perpendicularly and then returns along the same path. In the process, it passes through the polarizing beam splitter 74, the quarter-wave plate 76, the second plane mirror 38, and the quarter-wave plate 76 in sequence. In this process, it also passes through the quarter-wave plate twice, so the polarization state changes to vertical polarization. Then it is reflected by the polarizing beam splitter 74, then reflected by the first beam splitter 72, and enters the second photodetector 78 after passing through the second beam combiner 722.

[0091] The second polarizing laser 712 emits horizontally polarized light with a frequency of f2. After passing through the first beam splitter 72, the transmitted light passes through the polarizing beam splitter 74 and is then transmitted. The beam is perpendicularly incident on the first plane mirror 75, and then returns along the same path, passing through the polarizing beam splitter 74 and the first beam splitter 72 in sequence. After reflection, it passes through the second beam combiner 722 and enters the second photodetector 78. The two beams are combined in the second photodetector 78 to form a measurement interference signal.

[0092] This application achieves in-plane two-degree-of-freedom displacement measurement by making the reflector of the measurement optical path form an angle with the incident light, in conjunction with a single-axis laser interferometer. The measurement principle of this embodiment is explained theoretically below.

[0093] Simplified measurement systems such as Figure 7 As shown, the measurement system consists of a dual-frequency laser interferometer 37, a second plane mirror 38 with a fixed attitude angle, and a two-dimensional stage 05. The incident beam in the dual-frequency laser interferometer 37 is composed of two beams with frequencies of f1 and f2 and perpendicular polarization states. One beam is directly incident on the photodetector in the dual-frequency laser interferometer 37 as a reference beam, while the other beam, as the measurement beam of the dual-frequency laser interferometer 37, is incident on the second plane mirror 38 with a fixed attitude angle and then reflected back to the photodetector of the dual-frequency laser interferometer 37.

[0094] The complex amplitude of orthogonally linearly polarized light (including parallel polarized beam f1 and perpendicular polarized beam f2) output by a difference-frequency laser with a certain frequency difference. ( This can be represented as:

[0095] (1)

[0096] In the formula, φ0 and φ0 ， Let f1 be the initial phase of the parallel polarized beam and f2 be the vertical polarized beam, respectively, where E0 represents the amplitude and t is time.

[0097] The beam emitted from the dual-frequency light source, after passing through the beam-splitting prism, is reflected and enters the first photodetector to form a reference interference signal, which can be expressed as:

[0098] (2)

[0099] In formula (2), Δ φ = φ 0- φ 0 ’ Δ represents the difference in initial phase. f = f 1- f 2.

[0100] The beam emitted from the dual-frequency light source passes through a 7-beam splitter and is then transmitted to a polarizing beam splitter, where the vertically polarized light... f 1. When directly incident on an 8-biased mirror, it forms measurement light with a phase change, which is horizontally polarized light. f 2. After being reflected by the reference mirror, it serves as the reference beam. Therefore, the complex amplitude after the two beams coincide is expressed as follows:

[0101] (3)

[0102] In equation (3), E c , E m These represent the reference light and the measurement light received by the photodetector in the dual-frequency laser interferometer 37, respectively. φ 1. Describe the phase change introduced by the movement of the two-dimensional worktable 30.

[0103] It can be seen that the interference signal received by the photodetector in the dual-frequency laser interferometer 37 is:

[0104] (4)

[0105] When the two-dimensional stage (10) moves along the X-axis stepping direction, the measurement beam of the dual-frequency laser interferometer 37 will undergo optical path change, the general expression of which is:

[0106] (5)

[0107] In formula (5), S x This represents the displacement of the two-dimensional worktable 05 in the X direction. θThis represents the fixed attitude angle of the bias mirror. Since the measurement beam passes through the bias mirror twice, the optical path length of the measurement beam changes by a factor of 2. Therefore, the phase change caused by the movement in the X direction is:

[0108] (6)

[0109] In formula (6), λ R This is the center wavelength of the dual-frequency laser.

[0110] When the two-dimensional stage 05 moves along the Y-axis scanning direction, the change in optical path of the measurement beam of the dual-frequency laser interferometer 37 can be expressed as:

[0111] (7)

[0112] In formula (7), S y This represents the displacement of the two-dimensional stage 05 in the Y direction. Since the measuring beam passes through the second plane mirror 38 twice, the optical path length of the measuring beam changes by a factor of 2. Therefore, the phase change caused by the movement in the Y direction is:

[0113]

[0114] In formula (8), λ R Here is the center wavelength of the dual-frequency laser. From formulas (6) and (8), the displacement of the worktable can be obtained as follows:

[0115] (9)

[0116] Therefore, based on the above theoretical derivation, it can be seen that this application can calculate the displacement information in the horizontal and vertical directions by using a pre-set measuring reflector with a fixed attitude angle and a single-axis dual-frequency laser interferometer.

[0117] The optical components are assembled into a non-sequential ZEMAX configuration. The dual-frequency laser interferometer 37 uses a Gaussian light source with a wavelength of 628 nm, such as a heterodyne light source with wavelengths of 628.00682 nm and 628.00684 nm, with a beam diameter of 0.5 mm. The polarizing beam splitter prism 74 used for beam splitting has a diameter of 10 mm, the first plane mirror 75 and the third plane mirror 77 have an aperture of 8 mm, and the second plane mirror 38 has an aperture of 12 mm. The first photodetector 73 and the second photodetector 78 have a receiving area of ​​8 mm * 8 mm, and the receiver pixel size is 8 μm. In the initial optical path configuration, the distance between the first plane mirror 75 and the polarizing beam splitter prism 74 is 5 mm, and the distance between the second plane mirror 38 and the polarizing beam splitter prism 74 is 9 mm.

[0118] like Figure 8 As shown, when the second plane mirror has no tilt angle, (a) is the coherent phase grayscale image and coherent phase distribution map of the photodetector in the initial optical path state. (b) is the coherent phase grayscale image and coherent phase distribution map of the photodetector in the row section when the second plane mirror moves 1 mm in the negative X direction. (c) is the coherent phase grayscale image and coherent phase distribution map of the photodetector in the row section when the second plane mirror moves 1 mm in the negative Y direction. It can be seen that when the second plane mirror moves 1 mm in the negative X direction, the coherent phase in the photodetector changes; while when the second plane mirror moves 1 mm in the negative Y direction, the coherent phase in the photodetector does not change. Simulation verification shows that when the second plane mirror has no tilt angle, this measuring device can only measure the displacement information of the X-axis and cannot measure the displacement information of the Y-axis.

[0119] like Figure 9 As shown, when the tilt angle of the second plane mirror is 0.1°, (a) shows the coherent phase grayscale image and coherent phase distribution of the row section in the photodetector when the second plane mirror has no displacement information. (b) shows the coherent phase grayscale image and coherent phase distribution of the row section in the photodetector when the second plane mirror moves 1mm in the negative X direction. (c) shows the coherent phase grayscale image and coherent phase distribution of the row section in the photodetector when the second plane mirror moves 1mm in the negative Y direction. It can be seen that the coherent phase in the photodetector changes when the second plane mirror moves 1mm in the negative X direction and 1mm in the negative Y direction. Simulation verification shows that when the tilt angle of the second plane mirror is 0.1°, this measuring device can measure both the displacement information of the X-axis and the displacement information of the Y-axis.

[0120] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0121] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A single-mirror two-axis displacement measurement method applied to scanning interference fields, characterized in that, include: The output is a difference-frequency laser with vertical orthogonal polarization, the difference-frequency laser including a first polarized laser with a first frequency and a second polarized laser with a second frequency, the first polarized laser being horizontally polarized and the second polarized laser being vertically polarized; The first polarized laser is reflected by a first plane mirror as reference light into a first photoelectric detector; the second polarized laser is reflected by a second plane mirror and a third plane mirror as measurement light into a second photoelectric detector; wherein the bias angle of the first plane mirror is zero, the bias angle of the second plane mirror is not zero, and the bias angle of the third plane mirror is 2 . ​ Based on the interference between the measuring light and the reference light, the displacement of the object under test along the X direction in the two-dimensional plane is calculated. and displacement along the Y direction ,in, λ R The center wavelength of the difference frequency laser. This causes a phase change when moving in the X direction. The phase change is generated by the movement in the Y direction. The offset angle of the second plane mirror.

2. The single-mirror biaxial displacement measurement method according to claim 1, characterized in that, The offset angle of the second plane mirror It ranges from 0.05° to 1°.

3. The single-mirror biaxial displacement measurement method according to claim 1, characterized in that, The first polarized laser, after being reflected by the first planar mirror, is used as reference light and enters the first photodetector, including: The first polarized laser is reflected sequentially by the first beam splitter, the polarization beam splitter, and the first plane mirror, and then passes through the polarization beam splitter and the first beam splitter again before entering the first photodetector.

4. The single-mirror biaxial displacement measurement method according to claim 3, characterized in that, The second polarized laser, after being reflected by the second and third plane mirrors, is used as measurement light and enters the second photodetector, including: The second polarized laser sequentially passes through the first beam splitter, the polarization beam splitter, the quarter-wave plate, and the second plane mirror. After being reflected by the quarter-wave plate again, its polarization state becomes horizontal. It then passes through the polarization beam splitter again, is reflected by the third plane mirror, and returns along the same path. Finally, it passes through the first beam splitter and enters the second photodetector.

5. The single-mirror biaxial displacement measurement method according to claim 4, characterized in that, The distance between the second plane mirror and the polarizing beam splitter is greater than the distance between the first plane mirror and the third plane mirror and the polarizing beam splitter.

6. The single-mirror biaxial displacement measurement method according to claim 4, characterized in that, Also includes: The second planar reflector is rigidly connected to the two-dimensional plane of the object under test, so that the displacement of the object under test in the two-dimensional plane in the X and Y directions is measured by measuring the displacement of the second planar reflector in the two-dimensional plane.

7. The single-mirror biaxial displacement measurement method according to claim 3, characterized in that, Also includes: The first polarized laser and the second polarized laser enter the first photodetector through the first beam splitter to form a reference interference signal.

8. The single-mirror biaxial displacement measurement method according to claim 1, characterized in that, The output difference-frequency laser with perpendicular orthogonal polarization is either a dual-frequency laser or two independent single-frequency lasers.

9. The single-mirror biaxial displacement measurement method according to claim 8, characterized in that, When the output difference-frequency laser with perpendicular orthogonal polarization consists of two independent single-frequency lasers, a second beam combiner prism is also included, through which the reference light and the measurement light are incident on the second photodetector.

10. A single-mirror biaxial displacement measuring device applied to scanning interferometric fields, characterized in that, include: A laser that outputs a difference-frequency laser with perpendicular orthogonal polarization, the difference-frequency laser comprising a first polarized laser with a first frequency and a second polarized laser with a second frequency, the first polarized laser being horizontally polarized and the second polarized laser being vertically polarized; A first photodetector is used to receive the reference interference signal formed by the difference frequency laser. The second photodetector is used to receive the reference light and the measurement light to form a measurement interference signal; The reference optical path includes a first beam splitter, a polarizing beam splitter, and a first plane mirror; the first polarized laser is reflected sequentially by the first beam splitter, the polarizing beam splitter, and the first plane mirror, and then passes through the polarizing beam splitter and the first beam splitter again as reference light before entering the first photodetector. The measurement optical path includes a first beam splitter, a polarizing beam splitter, a quarter-wave plate, a second plane mirror, and a third plane mirror. The second polarized laser sequentially passes through the first beam splitter, the polarizing beam splitter, the quarter-wave plate, and the second plane mirror for reflection, then passes through the quarter-wave plate again, where its polarization state becomes horizontal. After passing through the polarizing beam splitter again, it is reflected back through the third plane mirror and returns along the original path, serving as the measurement light. It then passes through the first beam splitter and is coaxially incident on the second photodetector with the reference light. Wherein, the offset angle of the first plane mirror is zero, and the offset angle of the second plane mirror is... The offset angle of the third plane mirror is not zero, and the offset angle is 2. ; Based on the interference between the measuring light and the reference light, the displacement of the object under test along the X direction in the two-dimensional plane is calculated. and displacement along the Y direction ,in, λ R The center wavelength of the difference frequency laser. This causes a phase change when moving in the X direction. The phase change is generated by the movement in the Y direction. The offset angle of the second plane mirror.

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